PresbyLASIK is an excimer laser based method that is used to achieve a multifocal cornea that restores near vision in presbyopic patients. PresbyLASIK is also sometimes called multifocal LASIK because it works on principles virtually identical to the artificial multifocal lenses that provide vision correction for presbyopes, especially presbyopic cataract patients. Essentially, there are two types of presbyLASIK procedures. One is central presbyLASIK wherein a central disk is created for near vision and a peripheral ring is established for distance vision. The other is peripheral presbyLASIK wherein a central disk is created for distance vision and a mid-peripheral ring is created for near vision. It has been shown that the visual results of both types of presbyLASIK procedures compare favorably to the best pseudoaccommodation that could be theoretically achieved using multifocal refractive intraocular lenses. In these LASIK cases, however, there is still the possibility of introducing uncertainties that may compromise the final refractive outcome.
A recently presented procedure for introducing refractive corrections (e.g. the correction of presbyopia) into the cornea of an eye, without LASIK, involves the weakening of tissue in the stroma Specifically, such a procedure is disclosed in U.S. patent application Ser. No. 11/958,202 for an invention entitled “Method for Intrastromal Refractive Surgery,” (hereinafter the “'202 Appln”) which is assigned to the same assignee as the present invention As disclosed in the '202 Appln, the weakening of stromal tissue is accomplished using a pulsed femtosecond laser beam to create incisions in the stroma It can happen in a small number of cases, however, that these incisions may introduce annoying side-effects in night-vision (e g Halos, ring-patterns around bright light sources) Further, annoying side-effects may result inherently due to the multifocality of the reshaped cornea In any event, the unwanted side-effects are preferably overcome via neuro-adaptive suppression
In one of its aspects, neuro-adaptive suppression involves having the brain effectively ignore a visual perception For example, it can be demonstrated that a plethora of irregularities (e g stromal incisions) may be presented in a manner that will visually disguise an underlying regularity Insofar as an ophthalmic laser procedure is concerned, such a neuro-adaptive suppression may be very advantageous In particular, this will be so if the collective irregularities simultaneously accomplish a two-fold purpose For one, a pattern of collective irregularities must accomplish the same refractive correction that would otherwise be obtained by the underlying regularity alone For another, the pattern of irregularities needs to be visually illusive (i e obfuscate the underlying regularity), and thereby minimize any annoying visual side-effects (e g Halos) that might otherwise arise
In light of the above, it is an object of the present invention to provide a system and method for minimizing visual side-effects of a refractive surgical procedure that achieves a desired refractive correction with a pseudo-random pattern of irregular stromal incisions Another object of the present invention is to create a pseudo-random pattern of irregular stromal incisions, based on a statistical distribution, for correcting a vision defect with minimal residual side-effects Still another object of the present invention is to provide a system and method for minimizing visual side-effects of a refractive surgical procedure that is simple to use, relatively easy to manufacture, and comparatively cost effective.